Compositions that are activated by heat are known. For example, a common composition is a hot melt adhesive, which is heated to a liquid, or other flowable state, and applied to two articles to be secured together. Upon cooling, the composition becomes firm and provides adhesive properties that hold the articles together. The use of hot melt adhesives to secure two sheets of synthetic materials together is described in my earlier U.S. Pat. No. 4,861,404.
According to that earlier patent, the adhesive composition is also irradiated by a laser beam, which impinges on a line of the adhesive after it has been deposited onto the sheets of material to be secured together. The irradiation assists in obtaining a good bond between the adhesive and the material.
Irradiation of a surface hardening material before its application to a metal substrate is shown in U.S. Pat. No. 4,644,127 (LaRocca).
It is also known to pretreat a surface to be bonded (see U.S. Pat. No. 4,931,125 to Volkmann et al.) and to use a laser to heat and bond thermoplastic sheets (see U.S. Pat. Nos. 4,069,080 to Osborne, 4,636,609 to Nakamata, and 4,029,535 to Cannon).
The prior techniques suffer from several disadvantages. For example, the technique taught by 4,861,404 does not allow the energy of the laser to assist in melting the adhesive prior to its deposition, does not accommodate adhesive patterns other than straight lines, and permits cooling of the adhesive between application and subsequent heating by the laser. While the LaRocca patent shows laser melting of a metallic composition to be applied to a surface, it permits only minimal contact between the composition and the laser beam and does not facilitate following complicated patterns.